Electrophotographic apparatus



NOV. 26, 1968 Q L YOUNG v 3,413,063

ELECTROPHOTOGRAPHIC APPARATUS Filed March 28, 1966 ra Wel/0M 911g? i064@u goo fm IN VE N TOR. ('/MxzfsJ )fw/ v6 BLLMM United States Patent O3,413,063 ELECTROPHOTOGRAPHIC APPARATUS Charles J. Young, Princeton,NJ., assignor to Radio Corporation of America, a corporation of DelawareFiled Mar. 28, 1966, Ser. No. 537,964 3 Claims. (Cl. 355-14) ABSTRACT FTHE DISCLOSURE Apparatus for making a plurality of visible copies of anelectrostatic latent image on an insulating surface of a recordingelement comprises means to move the recording element along apredetermined path and a plurality of developing stations and copytransfer stations disposed sequentially along the path. The originallatent image is redeveloped for each transfer copy (in addition to thefirst copy desired).

This invention relates generally to electrophotography, and moreparticularly to improved apparatus for making multiple, visible,transfer copies from an electrostatic charge pattern. Th-e improvedapparatus is particularly useful for making a plurality of copies ofoutput data from computers whose outputs can be converted toelectrostatic charge patterns.

In an electrophotographic process of the type described in RCA Review,vol. XV, p. 469, December 1954, for example, an electrophotographicrecording element, comprising a layer of photoconductive zinc oxidedispersed in a resin binder on a backing of suitable conductivity, ischarged negatively so that the photoconductive layer carries a uniformelectrostatic charge over its surface. The recording element is exposedto a light image to discharge its surface in accordance with the lightintensity falling on it and to leave thereon an electrostatic latentimage. The latent image is developed by applying a finely dividedelectrically attractable toner, such as from an electroscopic mixture offusible toner palticles and iron tiling-s, thereon. The developed imagemay be fixed to the recording element by applying heat to the tonerparticles to fuse them on the recording element.

Previously, multiple electrostatic prints of an original have been madeby exposing successively a plurality of uniformly charged,electrophotographic recording elements to the same light image of theoriginal and developing each recording element separately. Suchapparatus for making a plurality of copies of the light image, however,requires the same light image to be available for each of the multipleexposures. In certain types of apparatus, as, for example, in computerswhere ouptut data is presented on the face of a cathode ray tube, thedata is usually presented for a time sufficient to make only one copythereof, thereby rendering the aforementioned prior-art apparatusunsuitable for providing multiple copies here.

In some other prior-art apparatus for making multiple copies, a numberof transfer copies are made from a single, untixed, developed original.Since only the amount of toner used to develop the original is availableto produce all of the transfer copies, each succeeding copy usually hasless contrast than the former.

It has also been proposed to provide apparatus for making a plurality oftransfer copies that utilizes only a single combination of a developingstation and a copy transfer station, but such an arrangement usuallyinvolves the use of reciprocating or recycling means that complicate theapparatus unduly.

It is an object of the present invention to provide improved apparatusfor making a plurality of developed` transfer copies of information thatcan be presented as an electrostatic image on a surface.

Another object of the present invention is to provide improved apparatusfor making multiple copies of an image, utilizing only a single exposureof the image.

Still another object of the present invention is to provide improvedapparatus for making a plurality of transfer copies of controllableand/or uniform contrast.

Briefly, the improved apparatus for making a plurality of developedtransfer copies of an image comprises means to move along apredetermined path an insulator member having an electrostatic chargepattern of the image on a surface thereof. A plurality of developing andtransfer stations, a separate transfer station being associated witheach developing station, are disposed successively along the path.Developing means are disposed at each developing station to apply tonerto the charge pattern to develop it, and transfer means are disposed ateach transfer station to transfer toner from the developed chargepattern to a transfer material, whereby to provide a transfer copy ofthe image on the transfer material. A transfer voltage may be providedat each transfer station, if necessary, to aid in transferring tonerfrom the developed charge pattern to the transfer material. Eachsuccessive transfer voltage may vary in amplitude to control the amountof toner transferred and to insure uniform contrast in each transfercopy, if so desired. Erasing means may be provided to remove anyremaining toner from the charge pattern after all of the transfer copieshave been made so that the insulating surface may be reused.

The improved apparatus will now be described in detail with reference tothe accompanying drawing, the single ligure of which is a schematicelevation of the improved electrophotographic apparatus.

Referring now to the drawing, there is shown improvedelectrophotographic apparatus 10 for producing a plurality of developed,transfer copies from a charge pattern on an insulating surface 12 of arecording element 14. The recording element 14 may comprise a backing ofsuitable conductivity, such as paper, having a moisture -content ofabout 546%, and the insulating surface 12 may be that of aphotoconductive layer of zinc oxide, as described in the aforementionedRCA Review. The recording element 14 is preferably in the form of anelongated web and is moved, by any suitable means, as by a motor 16 andsuitable coupling means, along a predetermined path from a supply roll18 to a take-up roll 20. Thus, the recording element 14 is unwound fromthe supply roll 18, and moved sequentially between rollers 22 and 24,around rollers 26 and 28, between rollers 30 and 32, and onto thetake-up roll 20. The arrows associated with the aforementionedcomponents indicate the directions of their movements.

A charging station 34 and an exposure station 36 are disposed along thepath of travel of the recording element 14 between the rollers 24 and26. Three developing and transfer stations 40, 42, and 44 are disposedalong the path of travel between the rollers 26 and 28, and erasingapparatus 46 is disposed at an erasing station 47 between the rollers 28and 30. In a typical example of operation of the .apparatus 10, therecording element 14 may be advanced along its predetermined path at arate of about 1,000 inches per minute.

The recording element 14 is charged uniformly as it passes through thecharging station 34. A negative corona discharge device S0 is disposedadjacent to one major surface of the recording element 14, preferablythe zinc oxide insulating surface 12, and a positive corona dischargedevice 52 is disposed adjacent to the other major surface of therecording element 14. The corona discharge devices 50 and 52 comprise adouble corona discharge device known in the art. When terminals 54 and56 of the negative and positive discharge devices 50 and 52 areconnected to the negative and positive terminals of a suitable powersupply (about 6,000 volts, not shown) the insulating surface 12 will becharged negatively with respect to the conductive backing.

A charge pattern, that is, a latent electrostatic image, of informationto be copied is formed at the exposure station 36 with the aid of athin-window cathode ray tube 58 of the type described in RCA Review,vol. XXII, No. 3, p. 582, September 1961. Briefly, the tube 58 is one inwhich information is provided on a transparent thin window 60 when astream of electrons within the tube 58 impinges upon a phosphor on thewindow 60. The output of the tube 58, that is, the image to be recorded,is determined by a character generator 62 electrically connected to thetube 58 in a manner well known in the art, and as explained in theaforementioned RCA Review. The character generator 62 may be a part of acomputer (not shown) for presenting information (images) to bereproduced by the apparatus 10. Thus, as the uniformly charged recordingelement 14 is moved across the thinwindow 60 of the tube 58, the zincoxide insulating surface 12 is rendered conductive by the light imageson the thin-window screen 60, whereby to produce charge patterns, i.e.electrostatic latent images, on the insulating surface 12. The relativespeed of the recording element 14 with respect to the exposure time atthe exposure station 36 is relatively slow so that the recording element14 can be exposed while it is in motion Without producing blurredimages.

The electrostatic latent image is developed and transferred to atransfer material for each transfer copy desired. In the apparatus 10,as illustrated herein, three developing and transfer stations 40, 42,and 44 are shown disposed along the path of travel of the charge patternbetween the rollers 26 and 2S. Although only three developing andtransfer stations 40, 42, and 44 are shown herein, merely forillustrative purposes, additional developing and transfer stations maybe included.

The combination of apparatus at the developing and transfer station 40is substantially similar in structure and function to that at each ofthe developing and transfer stations 42 and 44. Hence, only theapparatus at the developing and transfer station 40 will be described indetail, and the corresponding parts of the apparatus at the developingand transfer stations 42 and 44 will be designated with the samereference numeral plus the additional letters a and b, respectively.

A combination of developing apparatus 70 and transfer apparatus 72 isdisposed at the developing and transfer station 40. The developingapparatus 70 comprises a rotatable brush 74, such as a cylindrical brushof velour, disposed for rotation, by any suitable means, in a trough 76filled with developer 78, such as a triboelectric mixture of tonerparticles and iron filings. A wide belt 80, disposed between rollers 82and 84, serves to replenish the developer 78 with toner particles 86from `a hopper 88 as toner is consumed in developing the latentelectrostatic image. A vibrating mechanism 90 is mechanically coupled tothe hopper 88 to shake it and to cause the toner particles 86 to fallonto the belt 80.

The belt 80 is rotated by any suitable means connected to either one ofthe rollers 82 or 84. The belt 80 is disposed to contact the brush 74which, in turn, develops the latent image on the insulating surface 12of the recording element 14 by applying the toner particles from thedeveloper 78 to it. Any magnetic particles, such as the iron lings ofthe developer 78, that may adhere to the insulating surface 12, afterdevelopment, are removed by a magnetic system comprising iron rollers92, 94, and a magnet 96, such as an electromagnet. The rollers 92 and 94are rotated by any suitable means. Since the rollers 92 and 94 aredisposed closer to the insulating surface 12 than the magnet 96,magnetic particles are attracted to the rollers 92 and 94, are carriedout of the magnetic field as these rollers turn, and drop onto the brush94 or the belt 80 for eventual return to the developer 78 in the trough76.

After development of the latent electrostatic image, the unxed,developed image is transferred to a transfer material by the transferapparatus 72. The transfer apparatus 72 comprises two electricallyconducting rollers 98 and disposed on opposite sides of the recordingelement 14 along its path of travel. The roller 100 is connected to acommon connection, such as ground, and the roller 98 is connected to oneterminal 102 of a transfer voltage source (not shown), the otherterminal of the transfer voltage source also being connected to thecommon connection, ground.

If development of a direct charge pattern (latent electrostatic image)of a light image on the insulating surface 12 is desired, the roller 98is connected to the negative terminal of the transfer voltage source. Todevelop a reverse image, the roller 98 is connected to the positiveterminal of the transfer voltage source. If, for example, a pagecomprising black letters (image) on a white background is to be copied,a direct charge pattern of the image on the surface 12 is here definedas one which is formed by discharging the charge in the image area(letters). A reverse charge pattern of the image is one which is formedby discharging the charge in the image area, and retaining the charge inthe background area.

The rollers 100 and 102 are also mechanically biased toward each other,by any suitable means, as by springs (not shown) to apply pressurebetween the recording element 14 and a transfer material, such as atransfer sheet 104. At least one of the rollers 98 and 100 may be ofconductive rubber for good pressure contact. The transfer sheet 104 maybe in the form of an elongated web taken from a supply roll 106 andwound around the roller 98 so that it can come in contact with the unxeddeveloped latent image on the insulating surface 12 of the recordingelement 14. The motor 16 is mechanically coupled to the roller 100which, in turn, may be coupled to the roller 98 for moving the sheet 104at the same rate of speed as the recording element 14. (The motor 16 isalso coupled to the rollers 100a and 100b). Thus, a portion of theunlixed toner from the unixed, developed latent image is transferred tothe transfer sheet 104 to provide a first copy of the image. The imageon the transfer sheet 104 may be fixed, as by heat rays 108 from anysuitable source of heat.

The amount of electroscopic toner that may be transferred from anunfixed developed latent image on the insulating surface 12 to thetransfer sheet 104 may be controlled by a transfer voltage of suitableamplitude and polarity applied between the rollers 98 and 100, that is,across the transfer sheet 104 and the recording element 14. Thus, if theelectroscopic toner that is responsible for the development of thelatent electrostatic image is negative, the greater the :positivevoltage applied to the roller 98 with respect to ground the greater willbe the transfer of negative toner particles from the insulating surface12 to the transfer sheet 104.

Additional transfer copies can be made on transfer sheets 104g and 104bby redevoloping the charge pattern (latent electrostatic image) on theinsulating surface 12 with developing apparatus 70a and 70b, andtransferring toner from the unfixed redeveloped electrostatic images tothe transfer sheets 104a and 104b, respectively.

Since the charge of the latent electrostatic image on the insulatingsurface 12 tends to decay with time, uniformity of contrast of theimages on the transfer sheets 104a and 104b are assured by suitabletransfer voltages applied to the terminals 102a and 102b. In practice,where similar developer 78 is used for each transfer copy, it has beenfound that the transfer voltage for each additional transfer copy shouldbe increased to provide transfer copies of uniform contrast. Thus, ifthe transfer voltage applied to the terminal 102 is 600 volts, thevoltages applied to the terminals 102a and 102b may be in the order of650 volts and 750 volts, respectively.

While only three developing and transfer stations 40,

42, and 44 are illustrated in the apparatus 10 merely for illustrativepurposes, additional developing and transfer stations may be disposedalong the path of travel of the recording element 14, if so desired. Sixtransfer copies of substantially uniform contrast, for example, havebeen made easily from a single latent electrostatic image, utilizingapparatus similar to the apparatus but having six developing andtransfer stations instead of the three shown.

After the required number of transfer copies have been made, all of thetoner on the insulating surface 12 may be removed by the erasingapparatus 46. The erasing apparatus 46 comprises substantially a vacuumcleaner having a plurality of brushes 110, 112, 114 and 116 rotated byany suitable means in a hood 118 connected to any suitable Vacuumsystem. The cleaned recording element 14 is wound on the take-up roller20 and may be reused.

From the foregoing description, it will be apparent that there has beenprovided improved apparatus for making a plurality of visible transfercopies from a single charge pattern on an insulating surface. While theimproved apparatus has been illustrated with developing apparatuscarried out by electroscopic powder developer, variations of theapparatus, all coming within the spirit of this invention, will, nodoubt, suggest themselves to those skilled in the art. For example,liquid developing means for applying a liquid developer instead of apowder developer may be used to develop the latent electrostatic imageby any suitable means known in the art. Hence, it is desired that theforegoing description shall be considered as merely illustrative and notin a limiting sense.

What is claimed is:

1. In apparatus of the type wherein an electrostatic charge pattern ofan image is formed on an insulating surface, improved means for making aplurality of visible, transfer copies of said image comprising:

means to move said insulating surface along a predetermined path,

a plurality of image developing and image transfer combinationsstationed successively along said path, and

each of said combinations comprising developing means to apply toner tosaid charge pattern to develop it and transfer means to bring a transfermaterial momentarily into contact with the developed charge pattern totransfer at least a portion of said toner to said transfer material,

said transfer means comprising a pair of electrically conductiverollers, said transfer material comprising a sheet of paper, saidinsulating surface comprising the surface of a web of a recordingelement, said -path being between said pair `of rollers, and a transfervoltage applied between said pair of rollers, the transfer voltage ineach successive combination along said path being greater than that inthe previous combination.

2. In apparatus Vof the type wherein an electrostatic charge pattern ofan image on an insulating surface is developed by a toner, and at leasta portion of the toner of the developed image is transferred to a firsttransfer material at a transfer station to provide a first transfercopy, improved means for making a plurality of additional transfercopies of said image comprising:

a plurality of developing and transfer combinations,

means to move said insulating surface from said transfer station pasteach of said combinations in succession,

each of said combinations comprising developing means to redevelop saidelectrostatic charge pattern with a toner, and transfer means totransfer at least a portion of the toner from the redeveloped chargepattern to an additional transfer material,

said transfer means comprising a pair of electrically conductive rollersto press momentarily said addiditional transfer material against theredeveloped charge pattern and to apply a transfer voltage to said tonerto attract said toner from said surface to said transfer material.

3. Apparatus for making a plurality of visible copies of a latentelectrostatic image on an insulating surface of a photoconductive layerof a recording element, said apparatus comprising, in combination:

means to move said recording element along a predetermined path,

a charging station, an exposure station, a plurality of image developingand image transfer stations, and an erasing station disposedsequentially along said path,

a double corona charging device comprising a negative corona dischargedevice and a positive corona discharge device disposed on opposite sidesof said recording element to charge said insulating surface uniformly atsaid charging station,

a cathode ray tube having a screen for displaying information disposedadjacent to said insulating surface at said exposure station to exposesaid surface with a light image, whereby to form said latentelectrostatic image,

a plurality of image developing and image transfer combinations disposedat said plurality of image developing and image transfer stations,respectively, each of said combinations comprising developing means toapply toner to said latent electrostatic image on said surface todevelop it, and image transfer means to press momentarily a transfermaterial against the developed image, whereby to transfer at least aportion of the toner from said surface to said transfer material, saidtransfer means comprising a pair of electrically conductive rollersdisposed to receive said recording element and said transfer materialtherebetween,

means connected to said rollers to apply a voltage therebetween to aidin transferring said toner from said insulating surface to said transfermaterial, the transfer voltage in each successive combination beinggreater than that in the previous combination, and

cleaning means disposed at said erasing station to remove toner fromsaid insulating surface, whereby said recording element may be reused.

References Cited UNITED STATES PATENTS 3,115,814 12/1963 Kaprelian95-1.7 3,128,683 4/1964 Rubin 95-1.7 3,267,840 8/1966 Honma 95-1.7 X

JOHN M. HORAN, Primary Examiner.

